"We feel deeply indignant with the desecration of the grave of Soviet liberator soldiers in Sofia's Lozenets quarter by unidentified vandals overnight," the Foreign Ministry said.

"The sculptural composition and the wall with the names of buried soldiers was stained with red paint in several places.

"In connection with the outrageous act of vandalism, a note of protest was promptly lodged with the Bulgarian Foreign Ministry with a demand for taking measures to prevent such incidents in the future, bringing those responsible for breaching the law to justice and putting the grave and monument in order."

The monument was painted on the eve of the Bulgarian Socialist Party's celebration of its 123rd annivarsary, The Moscow Times reported.